Okay guys, I finally got this solved on my system. It had nothing to do
with BIOS settings, I was able to drop back to only 32 MB of RAM to the
onboard video.
I think the key seemed to be dropping back to nvidia-legacy-drivers (on
Gentoo), which is NVIDIA's version 7184. I have a buddy who says he's
running virtually the exact same hardware on the latest Gentoo
nvidia-drivers (8776, I think), so I suppose it's possible.
One thing that wasn't working for me at first when I was trying to go
back to 7184 was that I'd just see a tiny line of output at the very top
of the screen (X wouldn't crash though), and that was it. I finally
realized that was happening (apparently) because I was attempting too
high a resolution for my TV or whatever. When dropping back to 800x600,
things seemed to work fine.
Hopefully this helps someone struggling with the same thing, but
unfortunately I'm not able to describe *exactly* what happened to fix
it. All I know is that now I *can* use XvMC & GLX if I want, but don't
have to, either way I get none of those annoying tearing artifacts I was
seeing before.
If I come up with anything else, I'll try to remember to post it.
Thanks for the replies guys.
jl